Observation of prolonged ice algae bloom in drifting Arctic pack ice from autonomous buoy.

The WARM project uses autonomous ice-tethered buoys to collect data on biological processes and seasonal light penetration through the ice pack. In 2018 a ice algae bloom lasting 2 months was observed in drifting pack ice on the Chukchi shelf. At the time of buoy deployment ( March 29th 2018 at 72.3931N, -149.6E) the ice was 1 m thick with 7 cm of snow, light observed at the base of the ice was above reported levels for light saturating irradiance of ice algae. By April 11^th the bottom of the ice was experiencing 10 or more hours of light saturating irradiance each day. Ice algae growth became noticeable at the end of April and continued through into July. Light attenuation at the bottom of the ice was between 4 to 6 m^-1 (KdPAR), indicating an algae standing stock of between 100 to 300 mg CHL m^-2. Water column CHL did not reach above 5 mg m^-3, springtime new production was therefore, dominated by the ice algae community.

We use this data to explore whether the Arctic is entering an intermediate phase were thinner ice and less snow provides an early window for ice algae growth, perhaps inhibiting water column growth due to high light attenuation and/or nutrient drawdown.